HHFW Power Balance vs B and Antenna k
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HHFW Power Balance vs B and Antenna k || at Constant q J. Hosea, R. Bell, S. Bernabei, L. Delgado-Aparicio, B. LeBlanc, C.K. Phillips, P. Ryan, S. Sabbagh, K. Tritz, J. Wilgen, J.R. Wilson, et al. Goal: Measure RF power loss properties as a function of magnetic field at constant q to elucidate:

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HHFW Power Balance vs B and Antenna k|| at Constant qJ. Hosea, R. Bell, S. Bernabei, L. Delgado-Aparicio, B. LeBlanc, C.K. Phillips, P. Ryan, S. Sabbagh, K. Tritz, J. Wilgen, J.R. Wilson, et al.

Goal: Measure RF power loss properties as a function of magnetic field at constant q to elucidate:

  • RF power loss scaling with B under similar stability conditions

  • PDI ion heating loss vs B

  • Fast wave propagation characteristic effects on surface wave propagation and damping

  • Higher field should give higher efficiency of heating

    • PDI instability should be weaker at higher field

    • Onset density for propagation of HHFW is approximately proportional to B at a given k|| - waves are propagating farther from plasma edge at higher B

    • V Alfven scales with B - radial group velocity should increase with B so that wave propagation into core (away from surface) is faster - surface fields should decrease with B

    • May explain higher efficiency on DIII-D

  • Results from this experiment are important

    • Will help in making projections to the higher field regime of the ST CTF

    • Will provide support for increasing the k|| of the NSTX antenna for current drive phasing

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    0.20

    0.15

    PDI Losses Are Evident at Both k|| Values

    - Significant RF Power is Required to Sustain the Large Temperature Difference Between the Edge Ions and Electrons

    • Edge ion heating via parametric decay waves accounts for a substantial

    • amount of RF power loss which increases somewhat with wavelength -

    • 16%/23% loss for 14 m-1/-7 m-1

    T.M. Biewer et al., Physics of Plasmas 12 (2005) 056108


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    Propagation of fast wave begins at lower density for lower k||

    Propagating k vs density and k|| with B = 4.5kG

    k|| = 3m-1

    7m-1

    14m-1

    Density onset is

    function of ~ B*k||2

    • Propagation is very close to wall at 7m-1 and on the wall at 3m-1

    • Losses in surface should be higher for lower k||


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    B = 3 kG B = 5.5 kG

    VGpar

    VGpar

    VGper

    VGper

    This proposal is to study heating efficiency/power loss

    over the widest magnetic field range possible

    • 3 kG @ 400 kA and 5.5 kG @ 730 kA

    • Constant q is desired to control stability

    • Propagation onset density decreases a factor of two at the lower field

    • for both 7m-1 and 14m-1

    • Surface losses should increase substantially at the lower field - even at 14m-1

    • Perpendicular group velocity also decreases by a factor of ~ 2 - surface

    • fields should be enhanced further increasing edge losses

    • PDI losses can be expected to increase substantially at the lower field


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    Comparison of Thomson scattering measurements vs k|| at 5.5 kG and 3.0 kG

    Vertical

    Instability

    3.0 kG

    5.5 kG

    k|| = 14 m-1 7 m-1 -3 m-1

    • Te(0) is much larger at B = 5.5 kG for k|| = 7 m-1, Teo is also longer

    • Heating at -3 m-1 is still small at 5.5 kG

    • Vertical instability seriously affects the results at 3 kG for time > about 0.23 sec 


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    Comparison of Thomson scattering measurements vs k|| at 3.0 kG and 3.5 kG

    Vertical

    Instability

    3.0 kG

    k|| = 14 m-1 7 m-1 -3 m-1

    3.5 kG

    • Te(0) is significantly larger at B = 3.5 kG for k|| = 14 m-1

    • Instability still seriously affects the results at 3.5 kG for time > about 0.25 sec 


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    B = 3.5 kG

    B = 5.5 kG

    TiHOT

    Time (sec)

    Time (sec)

    B = 3.0 kG

    ERD TiHOT vs Band k|| at R = 145 cm

    Helium, PRF = 2 MW

    TiHOT

    k|| = -3m-1

    k|| = -7m-1

    k|| = 7m-1

    k|| = 14m-1

    • Reduction in TiHOT at higher field,

    • especially at k|| = 14 m-1

    • Reduction at lower field perhaps due to

    • hot ion loss or vertical instability

    Time (sec)


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    RF Probe Signals are a strong function of k||

    BRF

    (au)

    B= 5.5 kG

    PRF = 2 MW

    k|| = -3m-1

    -7m-1

    14m-1

    Time (sec)

    • BRF at Bay J midplane increases by a factor of ~ 3 for a decrease in

    • k|| from 14m-1 to -3m-1

    • This could give rise to around an order of magnitude increase in structure/sheath losses

    • Fluctuation level at high power appears to be large


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    Good Heating Observed for k|| = -7m-1 at B = 5.5 kG

    -- Teo > 3.6 keV for PRF = 2 MW

    TS

    fOSXR

    ERD

    • TiHOT and Ti1G evolve somewhat during pulse

    • - but do not see core collapse

    • BRF also evolves smoothly (0.012 - 0.016)

    • Fast time behavior of Te(0) is indicated by

    • fast OSXR diagnostic

    • MHD is observed at the core temperature

    • collapse


    Expected results

    Expected Results

    • Heating efficiencies vs B for 14 m-1, -7 m-1 (co CD) and 7 m-1 ( phasing)

      • Core heating from EFIT W

      • Core electron heating from Thomson scattering

    • Edge heating/power loss

      • Edge ion heating from edge rotation diagnostic

      • Edge electron heating from Thomson scattering

    • Behavior of PDI characteristics and induced losses with field

    • Plasma profiles , core and edge, for permitting predictions of wave propagation and damping characteristics and of PDI produced losses

    • Relative surface wave amplitude for comparison to surface power loss for the explored conditions

    • Ceramic gap RF emission for the explored conditions


    Planned analysis

    Planned Analysis

    • Calculation of  and W for EFIT W to obtain percent PRF deposited

    • Calculation of e and We for Thomson scattering We to obtain PRF delivered to electrons

    • Compare efficiencies for the two field cases

    • Analysis of wave propagation and damping characteristics from onset density into the core of plasma - along field and perpendicular directions of the ray path, and including collisions - for predicting surface losses

    • Development of predictions for PDI losses

    • Projection of heating efficiency expected at 10 kG, with and without PDI present, to compare with DIII-D results and for higher field ST devices

    Preliminary Conclusions

    • HHFW heating decreases with decreasing k|| and improves with B

    • PDI edge heating is a relatively weak function of B except for 14 m-1

    • Edge RF B field is strongly dependent on k|| suggesting surface waves

    • could contribute significantly to RF power losses

    • In future, we need to determine RF B toroidally and poloidally as function

    • of B and look at FFT spectra to evaluate edge turbulence

    • We should increase current drive k|| to improve CD efficiency

    • Also, preliminary analysis suggests that increasing the frequency would

    • greatly reduce the PDI heating


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